Opacification of paint

ABSTRACT

Aqueous flat paints are disclosed having improved hide at lowered titanium dioxide content in which the dispersed pigment is present in an amount providing a pigment volume concentration of from 60% to 80%, and in which the pigment contains from 5% to 25% of titanium dioxide, rutile, and the balance of the pigment consists essentially of pigmented vesiculated beads and opaque polymer particles in a ratio of 80/20 to 90/10. The small proportion of opaque polymer particles used minimizes the reduction in burnish and scrub resistance, but a large gain in hide is obtained.

DESCRIPTION

1. Technical Field

This invention relates to the pigmentation of paint using a plurality ofopacifying agents in order to enhance the hiding quality of the paintwhile minimizing the proportion of titanium dioxide which is present aswell as the undesired softening of the paint.

2. Background Art

A conventional paint comprises a resinous binder which serves to holdtogether particles of pigment. These particles of pigment obscure theimperfections in the surface of the substrate which is painted, and thisobscuring capacity is known as "hide". In modern paints, heavy relianceis placed upon the use of titanium dioxide, rutile, as the pigmentbecause it contributes excellent hide. Unfortunately, this pigment isexpensive.

Because of the expense of the titanium pigment, other pigments have beendeveloped, including pigmented vesiculated beads and opaque polymerparticles. Both of these are known articles of commerce for use in thepaint industry and are less costly than titanium dioxide. However, thepigmented vesiculated beads do not entirely maintain the hide which isreduced in proportion to the amount of titanium which is replaced. Theopaque polymer particles do enhance the hide, but these are soft and,when used in large amount, degrade the burnish resistance and scrubresistance of the final paint film.

DISCLOSURE OF INVENTION

In accordance with this invention, an aqueous flat paint having improvedhide at lowered titanium dioxide content comprises water, a resinbinder, and pigment dispersed in the water, this pigment being presentin a pigment volume concentration (PVC) of from 60% to 80%, and thepigment contains from 5% to 25% of titanium dioxide, rutile, with thebalance of the pigment consisting essentially of pigmented vesiculatedbeads and opaque polymer particles in a ratio of 80/20 to 90/10. Byblending a large proportion of pigmented vesiculated beads with a smallproportion of opaque polymer particles in the described combination,very little opaque polymer is present in the paint, and the burnishresistance and the scrub resistance remain high. At the same time, ifthe replacement of the titanium dioxide is entirely by pigmentedvesiculated beads, the improvement in hide would be less than about 20%of that obtainable using opaque polymer particles as the solereplacement of titanium dioxide. However, the blends of this inventionin which only 10% to 20% of the volume of the mixture is opaque polymerparticles provides about 60% or more of the hide improvement obtainableusing opaque polymer particles as the sole replacement for the titaniumdioxide.

All proportions and ratios herein are volume proportions based on drysolids, unless otherwise specified.

This invention is applicable to paints in which the resin is dissolvedor colloidally dispersed in the aqueous phase of the paint, but theinvention is primarily adapted to latex paints in which the resin binderis constituted by particles of solid resin suspended (emulsified) in theaqueous continuum with the aid of a surfactant.

This invention is specifically concerned with "flat" paints. This termis well known in the latex paint industry and denotes a paint whichdeposits a film which, when dry, exhibits a gloss not in excess of 6regardless of whether a 60° or 85° gloss meter is used to determine theproportion of light which is reflected. Thus, the mixture of pigmentsused herein is required to provide a paint having rather specificproperties.

The opaque polymer particles employed herein are emulsion polymerparticles of generally transparent water insoluble polymers having asufficiently high glass transition temperature to avoid coalescence inthe aqueous paints which are involved. These polymer particles have anaverage particle size in the range of 0.1-2.5 microns and containmicrovoids which scatter incident light and thereby produce opacity.These microvoids can be provided in various ways, conveniently by firstpolymerizing in aqueous emulsion a swellable core polymer containingcarboxylic acid groups, typically provided by from 5% to 50% by weightof acrylic acid or methacrylic acid, which enable the core to be swollenwith a volatile amine or ammonia. A sheath of polymeric material is thenemulsion polymerized around the acid-containing core. The sheathedparticles are subjected to the volatile amine or ammonia in aqueousdispersion to swell the core, and the dispersion is dried to remove theswellant and provide a microvoid within the sheathed polymer particle.Typical opaque polymer particles and their production are disclosed inEuropean patent application having Publication No. 0022633 A2 of Rohmand Haas Company. The microvoid-containing product of Example 1C of thatdisclosure is identified herein as opaque polymer A and will be used inthe Examples of this application. In opaque polymer A, the core is acopolymer of 69.65% methyl methacrylate, 29.85% methacrylic acid, and0.5% ethylene glycol diacrylate having an average particle diameter of0.35 micron. This core has a swell ratio at pH 10 with ammonia of around12, by volume. The described core is sheathed with polymerized methylmethacrylate to an average diameter of 1.0 micron and the sheathedparticle is neutralized with ammonium hydroxide and heated to 95° C. toswell the particles to 1.15 micron before the ammonia is evaporated toprovide an internal void.

The pigmented vesiculated beads which are used herein are generallylarger than the opaque polymer particles and contain a plurality ofsmall cells or vesicles whose walls are provided by the polymer of thebeads. These beads have an average particle diameter of from 3 to 30microns and contain from 10% to 60%, preferably from 30% to 55%, byweight (dry) of finely divided pigment, usually titanium dioxide,rutile. These vesiculated beads are available in commerce and aredescribed in Kershaw et al. U.S. Pat. No. 3,933,579 dated Jan. 20, 1976.They are generally spheroidal with a ratio of bead diameter to meanvesicle diameter of at least 5:1.

The pigment volume concentration (PVC) is important to the provision ofa superior flat paint. The narrow range of PVC described previously isthus a necessary aspect of this invention.

The small proportion of titanium dioxide used herein is also important.In preferred practice, the proportion of titanium dioxide, rutile, isfrom 7% to 15%. This is especially important from the standpoint ofminimizing the cost of the paint.

The intended use of the paint, such as for interior or exteriorapplication, does not change the parameters of this invention. However,air dry paints are primarily contemplated herein because elevated curingtemperatures which destroy the voids in the opaque polymer particleswhich help to create the desired opacity are counterproductive to thisinvention.

It should be appreciated that it is common in latex paints to include aproportion of extender particles which contribute little to the hide.Such extender particles, illustrated herein by silica or calciumcarbonate, are commonly present in amounts up to about 30% of the totalparticulate content of the paint, but these do not alter the synergismof this invention.

It will also be evident that while the three pigments noted herein areto provide the desired opacity, one may still wish to add small amountof other pigments or colorants for special purposes, such as to providethe desired coloration or to confer other optical effects. Thus, thepigmentation consists essentially of the three pigments which have beendiscussed since these determine the hiding capacity of the paint.

The invention will be illustrated in the examples which follow.

EXAMPLE 1 Flat Paint (non-extended)

    ______________________________________                                                                         Gallons                                      Component      Lbs.     Gallons  (non-volatile)                               ______________________________________                                        Titanium Dioxide, rutile                                                                     100      3.1      3.1                                          opaque polymer particles                                                                     53.6     6.2      3.15                                         pigmented vesiculated                                                                        375      39.4     17.4                                         beads                                                                         Acrylic latex  138.8    16.0     7.9                                          Additives      61.4     4.2      2.1                                          Water          259.5    31.2     0                                            ______________________________________                                    

This paint has a PVC of 75%, titanium dioxide constitutes 13% of theprime pigmentation and the ratio of pigmented vesiculated beads toopaque polymer particles is 85/15. The burnish resistance and scrubresistance are essentially the same as the same paint pigmented withonly titanium dioxide, but the hide is almost as good despite the smallamount of opaque polymer present.

EXAMPLE 2 Flat Paint (extended)

    ______________________________________                                                                         Gallons                                      Component      Lbs.     Gallons  (non-volatile)                               ______________________________________                                        Titanium Dioxide, rutile                                                                     50.92    1.58     1.58                                         opaque polymer particles                                                                     47.31    5.50     2.78                                         pigmented vesiculated                                                                        317.73   33.34    14.77                                        beads                                                                         Silica Extender                                                                              100.33   4.55     4.55                                         Acrylic latex  138.78   15.96    7.90                                         Additives      61.40    4.20     2.14                                         Water          290.47   34.87    0.00                                         ______________________________________                                    

This paint has a PVC of 75%, titanium dioxide constitutes 8% of theprime pigmentation and the ratio of pigmented vesiculated beads toopaque polymer particles is 84/16. The extender is 19% of the totalpigmentation. Extender may be added up to 30% of pigment volume toimprove film properties, as long as the prime pigment ratios of titaniumdioxide, opaque polymer particles and pigmented vesiculated beads aremaintained. Again, the burnish resistance and scrub resistance areessentially the same as the same paint pigmented with only titaniumdioxide, but the hide is almost as good despite the small amount ofopaque polymer present.

Note 1

In both examples, the opaque polymer particles were provided by acommercial product called Rhopaque OP-42 marketed by Rohm and Haas ofPhiladelphia, Pa.

Note 2

In both examples, the pigmented vesiculated beads were provided by acommercial product called Spindrift PVB made by The EnterpriseCompanies, Wheeling, Ill.

Note 3

The acrylic latex used in both examples is AC-388 made by Rohm and Haas.

Note 4

The additives are those normally used in the production of paints, andinclude surfactants, thickeners, preservatives, fungicides, coalescingsolvents, materials for the adjustment of pH, defoamers and driers.These are of no consequence in this invention.

What is claimed is:
 1. An aqueous flat paint having improved hide atlowered titanium dioxide content comprising, water, a resin binder, andpigment dispersed in the water, said pigment being present in an amountproviding a pigment volume concentration of from 60% to 80%, saidpigment containing from 5% to 25% of titanium dioxide, rutile, and thebalance of the pigment consisting essentially of a mixture of pigmentedvesiculated beads and opaque polymer particles in a ratio of from 30/70to 90/10, said opaque polymer particles having a glass transitiontemperature high enough to avoid coalescence in the aqueous paint, anaverage particle size in the range of 0.1-2.5 microns and containinglight-scattering microvoids which provide these particles with theiropacity.
 2. An aqueous paint as recited in claim 1 in which said binderis an emulsion copolymer suspended in the water with the aid of asurfactant.
 3. An aqueous paint as recited in claim 1 in which theproportion of titanium dioxide, rutile, is from 5% to 15% of totalpigment.
 4. An aqueous latex paint as recited in claim 2 in which theproportion of titanium dioxide, rutile, is from 5% to 15% of totalpigment.
 5. An aqueous latex paint as recited in claim 4 in which saidpaint is an air drying paint.
 6. An aqueous paint as recited in claim 1in which said vesiculated beads have an average particle diameter offrom 3 to 30 microns and contain from 10% to 60%, based on their dryweight, of finely divided pigment.
 7. An aqueous paint as recited inclaim 6 in which the finely divided pigment in said vesiculated beads istitanium dioxide, rutile.
 8. An aqueous paint as recited in claim 1 inwhich the total pigmentation includes up to about 30% of extenderparticles.